1. Field of the Invention
The present invention relates in general to an improved process for the preparation of camera-ready mechanicals for color printing. More particularly, the present invention relates to an improved electronic prepress process which facilitates the integration of both visual and textual and both black and white and color inputs from various sources into a final set of output files which can be read by a raster image processor as a process step in the creation of camera-ready mechanicals for printing.
2. Description of the Prior Art
The printing process is comprised of several discreet process steps which can be summarized as follows:
Prepress--the term which is used to describe all aspects of production up to preparation of the camera-ready mechanicals or film, prior to making the printing plate; PA0 Platemaking--the process of converting a camera-ready mechanical or film into a printing plate; PA0 Printing--the act of impressing the plate upon printing paper to reproduce the image on the plate or paper or other print medium; PA0 color separation; PA0 color correction; PA0 screening (halftones); PA0 retouching; PA0 image manipulation; PA0 page assembly.
The invention is directed to the prepress process step of print reproduction.
The color prepress process, i.e. all of the production activities leading up to preparation of the camera-ready mechanicals or film for color reproduction involves the following basic steps:
The use of electronic components has greatly facilitated the carrying out of the foregoing process steps.
An excellent description of the electronic color prepress process is presented in Publish! Magazine May 1989 at p. 44-49.
By laying down just three colors in correct proportions, it is possible to reproduce full-color images. The three colors used are yellow (y), magenta (m), and cyan (c). They are called subtractive primaries because each results from the subtraction of one of the additive primaries red, green, and blue that make up white light.
Full color art is "separated" into its red, green and blue components. Three separate photographic exposures are made using corresponding filters. The result is three separate negatives; i.e., black and white maps of where the red, green, and blue components of the picture lie. These are used to expose positive printing plates; one for cyan, one for yellow, and one for magenta. Cyan ink blocks (absorbs the wavelengths of) red light and transmits (reflects) blue and green. Yellow blocks blue and transmits red and green. Magenta blocks green and transmits blue and red. Basically color process printing involves laying down the corresponding subtractive primary ink in areas where the additive primary does not appear in the original. Therefore, for example, cyan should be printed in all areas where red does not appear in the original (which corresponds to the non-image area of the separation negative and the image area of the positive printing plate).
When all three colors are laid down in the proper areas, the result will appear to reproduce the original color range. In areas where only one subtractive ink prints, one additive primary will be blocked out and the other two will be reflected. Where two subtractive primaries print, all but one additive primary will be blocked out. For example, wherever cyan (blocks red) and magenta (blocks green) print, only blue will appear. Where all three subtractive primaries print, all three corresponding additive primaries will be blocked out, and the result will be black.
Because of imperfections in the physical nature of printing inks, not all colors are absorbed and transmitted as neatly as in theory. For this reason, colors will often appear muddy or contaminated with other hues. For example, reds usually appear orange and blacks appear greyish. The addition of a fourth print for black ink (k) is therefore necessary to enhance sharpness and color fidelity, and eliminate the problems associated with muddiness and color contamination.
The converse problem to muddiness and hue adulteration in the physical printing process is the problem of inexact registration when various colors and objects are juxtaposed with one another. Registration is defined as the placing of an object or hue next to another object or hue in such a manner that there is no break in the continuum of color and object. If the colors merely "bumped" into one another, a gap would occur when registration was not perfect, causing a result which is considered to be undesireable from a professional printing point of view. This problem is solved by a process called trapping wherein, in conventional prior art processes, the process colors (cmyk) of underlying shapes of a design are made to "bleed" into the colors of overlaying shapes.
The electronic prepress process which involves optically scanned images in combination with a page description language resulting in Bit-Mapped color image files as output eliminates many of the problems associated with inexact registration insofar as the negatives which are used to create the mechanicals for printing will all contain all four colors so that when one image is placed next to another image there will be continuity of color from one image to the next, thereby precluding the appearance of a gap between images.
The problem of inexact registration within the context of the electronic prepress process occurs when one image which does not contain the full color spectrum is juxtaposed with another image which does not contain the full color spectrum. In such situations, it is possible that insufficient overlap of images (i.e., inexact registration) will cause the appearance of a gap between images because of discontinuity in the color spectrum of the two images. This occurs when the images which are created in the prepress process emanate from various types of draw and graphics package software.
The starting point in the color prepress process is the capturing of the original image to be reproduced. This original image may emanate from different sources such as optically scanned input, or textual input via word processing at a "PC" or "MAC" workstation, or from various types of draw package software which may be utilized to create the image at an electronic work station.
These multiple inputs from different points of origination each have different functions, different features, different limitations, and different ways in which their input protocols are structured, and hence are to a significant extent incompatible. For example, draw packages were designed to function in a color environment while page layout software was originally designed for a black and white environment. Additionally, in situations wherein it is desired to overlay portions of one figure in an image with another figure of a different color, camera-ready mechanicals produced with electronic publishing systems having a central processing unit in the $6,000 price range, have here-to-fore produced printing plates wherein the fidelity of the color of the superimposed image was adulterated because of the partial transparency of printing inks which allowed the underlying color to show through the overlaid color. Additionally, the prior art processes, have required multiple sets of negatives which, when utilized in the "make ready" process, (i.e., the laying down and "stripping" of sets of negatives in preparation for the making of printing plates) have all required multiple preparations of sets of negatives for the combination of colors which it was desired to reproduce. For example, previously it has been necessary to produce at least two sets of four copies of C,M,Y,K negatives in electronic prepress processes which were directed to systems at the $6,000 central processor level.
In accordance with the present invention, a methodology is described for accomplishing electronic "bleeding" for the trapping process involving images derived from draw and graphics packages and integrating the input derived from various incompatible sources and manipulated by numerous types of incompatible software, into a final set of output files which can be read by a raster image processor output device, thereby eliminating the problems associated with multiple incompatible inputs into the electronic color prepress process disclosed in the prior art at the $6,000 central processing unit level.